This invention relates generally to scales suitable for industrial applications such as batch weighing and loss-of-weight metering of particulate solid materials ranging from highly fluid powders to corrosive chemicals and abrasive ores. More particularly, the invention relates to an improvement in the stability of calibration of weighing suspension scales under variable shock and overloading conditions, varying positions of loads on the scale, and deformation of support structures.
U.S. Pat. No. 3,477,533 issued to the present applicant and Peter J. Tolan, dated Nov. 11, 1969, describes suspension weighing apparatus of a type that has come into wide use. A load platform in the form of a hopper having a valve, gate or volumetric feeding element at the bottom is suspended on a load transfer linkage by a first set of vertically hanging suspension members such as wire rope cables. The linkage includes a pair of torsionally rigid torque transmitting members which are in turn suspended from a fixed support frame by a second set of vertically hanging fulcrum suspension members. The axes of suspension of the first set of suspension members are spaced from the axes of suspension of the second set of suspension members, forming torque arms, whereby the load on platform applies torques to the horizontal members. The torque transmitting members have attached equalizing lever arms arranged to transfer the torque on one member additively to that on the other. The linkage of the torque transmitting members thus completed is counterbalanced by means including a load cell that applies and indicates a force proportional to the sum of the torques applied through the suspension members.
For acceptable reliability in use of the scale described in the patent, close tolerances are required in the manufacture of the scale and particularly the load transfer linkage and suspension member connections. It is necessary not only that the torque transmitting members are torsionally rigid, but that the suspension members are vertical and that the axes of the load platform supporting suspension members are equally spaced at all points of suspension from the axes of the fulcrum suspension members attached to the support. Past efforts to control this spacing have included the use of torque tubes with the suspension members partially wrapped over the tube surfaces, with reliance on the tube diameters to control the spacing. In many applications, these efforts have been found unsatisfactory, particularly when the scales are subjected to shocks or overloading, due to high surface compressive stresses on the suspension members where in contact with the torque tubes. Under these stresses the cross sections of the suspension members are often subjected to distortions leading to loss of calibration, nonuniformity of response at the points of suspension, and sensitivity to the position of the load on the scale.
In scale structures of the type described in the above patent, where the suspension members are not in contact with the torque tubes but are attached to members secured on the tubes, improvements in the stability of calibration are obtainable only by means of close tolerances in the manufacture and assembly of the parts forming the load transfer linkage. This adds significantly to the cost of manufacture.
Accordingly, the principal object of this invention is to provide a load transfer linkage constructed to improve the stability of calibration of suspension scales reliant on the use of torque transfer members, and in particular the spacing of the vertically extending suspension members.
A second object is to achieve the desired stability of calibration by means of structures that are easily and relatively inexpensively fabricated and assembled.
The foregoing and other objects of the invention will become apparent from the following description.